The invention relates to a control device of an electromagnet comprising at least one holding coil connected in series with an electronic switch to the terminals of a supply voltage of the coil, means for measuring the holding current flowing in the holding coil, control means for controlling the electromagnet comprising means for regulating the holding current connected to the means for measuring the holding current and to a control electrode of the electronic switch, and power supply means of the control means.
Circuit breakers generally comprise a certain number of electrical auxiliaries, more particularly closing electromagnets (XF) or opening electromagnets. Two types of opening electromagnets, or voltage trip releases, are generally provided. They comprise an electromagnet which must be actuated when certain conditions having to cause opening of the circuit breaker are met with. An under-voltage release (MN) causes opening of the circuit breaker when the voltage of the power system to be protected drops below a certain threshold, and a shunt release (MX) causes opening of the circuit breaker when the power system voltage exceeds another threshold.
For control of an electromagnet, it is known (FR-A-2,133,652) to temporarily supply a relatively high inrush current, followed by a lower holding current. This can be achieved either with a device comprising a single coil, in which the current is switched to constitute the holding current, or with a double coil formed by an inrush coil and a holding coil. It is also known to regulate the inrush and holding currents to preset levels (FR-A-2,568,715). This device is supplied by a power supply circuit which dissipates a non-negligible power and is therefore both costly and voluminous.
Voltage supply of the circuits of a control device of an electromagnet may require production of an auxiliary supply voltage. The document EP-A-353,533 proposes using for this purpose the voltages induced in a control coil of the electromagnet when the transistors connected in series with the coil are turned off. This embodiment does not enable the current flowing in the coil to be regulated since a part of this current is branched off to the power supply circuit.